96 J. W. SPENCER ON 



great efficiency in eroding lake-basins. To this scepticism, it seems to me that these 

 notes must contribute ; especially when glacial erosion is applied to the hypothetical 

 excavation or modification of great lake-basins, and the transportation of the northern 

 materials in the boulder clay over the broad plains of America, as there were no mountains 

 of adequate height with i^eaks, or séracs, to supply the detritus sufficient to furnish the 

 tops of the glaciers with all the boreal material of the drift, which "covers half a 

 continent." 



In connection with this paper, the observations of Herr Payer and other arctic 

 explorers are important. The snow-line of Franz Joseph Land descends to within a 

 thousand feet of the sea, and the numerous glaciers discharge great quantities of icebergs 

 as they move down into the ocean. Payer says : " However diligently I looked for them, 

 I never saw uumistakeable traces of grinding and polishing of rocks by glacier-action." ' 



Lieut. Lockwood ' found in central Grrinnell Land a thick ice-cap, extending for a 

 distance of from seventy to ninety miles, faced by an ice-wall from 125 to 200 feet high, 

 irrespective of topographical inequalities. It was free from rock debris, except in a valley 

 confined by mountain-walls thousands of feet high. Along its foot there was almost an 

 absence of morainic deposits, and even where present these were lyiimportant ridges. The 

 general absence of rock and dirt in the arctic glaciers is a common subject of remark. 

 The snow line in the high latitude of central Griunell Land is 3,800 feet above the sea, 

 and the glaciation of the rock about the adjacent Lake Hazen (500 feet above tide) is not 

 recent. 



In Spitzbergen, where the snow-line is much higher, striated rocks according to 

 Nordeuskjold occur only below 1,000 feet. ^ The same holds true for Labrador, where the 

 scratches are confined to the lower thousand feet, although the mountains rise to 6,000 

 (Bell.) ' 



In the Antartic regions, the officers of the " Challenger " remarked the absence of 

 detritus in the icebergs and southern ice, although "Wilkes and Ross saw rocks upon a few 

 bergs. These last are supposed to have come from A^alleys in the A'olcanic mountains. 



Indeed, outside of valleys, explorers in high latitudes have not found, iti the margins 

 of such ice-caps visited, the tools capable of great erosion. The continental ai-ea of North 

 America presents very much lower and less abrupt prominences than the reliefs of G-reen- 

 laud, Grinuell Land, Spitzbergen or Franz Joseph Laud. Overhanging mountains seem 

 to be necessary to supply glaciers with tools by which alone any abrasions can be accom- 

 plished, and these conditions belong only to valleys of great mountain ranges. However, 

 there is one condition under which glaciers, when shod with graving tools ought to be 

 great eroders, viz., when their motion is much more rapid than the flow of land ice, — 

 which is almost invariably less than three feet a day, under which condition, included 

 stones commonly adhere by friction to the subjacent rocks, and cause the lower surfaces 

 of the ice to be grooved. This condition of extraordinarily rapid movement has been seen 

 at Jacobshavn glacier in Greenland, where Prof Helland '' found a A^elocity of from forty 

 to sixty feet a day. In Alaska, Lieut. Schwatka " and Prof. G-. F. Wright ^ observed 



' New Lands Within the Arctic Circle, 1872-74. ' Three Years of Arctic Service 1881-4, Greely. 



^ See Geological Magazine, 1876. ' Dr. Robert Bell, in Hudson's Bay Expedition of 1884. 



^ Ice-fjords of North Greenland, Quart. Jour. Geo. Soc, 1S77, A. Holland. 



« " Times" Alaska Expedition, New York, 1886, Schwatka. ' The Muir Glacier, Am. ,Iour. of Sci., 1887. 



